The present invention relates to the field of mobile radiocommunications.
It applies to networks in which the infrastructure is distributed between on the one hand a core network, which manages the data and states relating to the mobile subscribers and which provides the appropriate interfaces with the fixed transport networks, and on the other hand an access network comprising radio relays, or base stations, and their control equipment for managing the radio resources employed.
The invention applies in particular to cellular networks. In the case of GSM systems and derivatives, the access network is called the base station subsystem (BSS), and the core network includes mobile switching centers (MSC) for circuit mode communications and GPRS support nodes (GSN) for packet transmissions (GPRS, “General Packet Radio Service”). The invention is also applicable to third-generation cellular networks such as UMTS (“Universal Mobile Telecommunications System”).
It is assumed that a mobile station (regarded as the combination of the mobile equipment or terminal and any subscription on which it acts) is essentially characterized in the access network by its active or inactive state.
When a mobile station is inactive for the access network, the latter does not store any specific data relating to this mobile station. A mobile station is thus regarded as inactive when it is off, or when it is on but out of range of a base station. Another case of inactive mobile station is that of an idle station, in which the station is on and within range of one or more base stations but without it being taken into account by the access network. In idle mode, a mobile station monitors, in particular, broadcasting channels over which the base stations transmit beacon signals, so that the best base station with which it is able to communicate is determined. It can on the other hand receive a certain number of services, among which may be mentioned “paging”, by which the core network enquires as to the availability of a mobile station and may instruct it to adopt a certain behavior (for example in view of setting up a communication), or else the broadcasting of short messages (SMS-CB, “Short Message Service—Cell Broadcast”), etc. To supply such services to the idle mobile stations, for which it has no information, the access network uses communication resources (generally radio broadcasting channels) shared with a certain number of other mobile stations, also unknown to the access network. The service will be provided if the mobile station is actually idle in a cell whose base station has used the resources in question.
In active mode, a context relating to the mobile station is taken into account in the access network. Part of this context refers to the particular means of communication allocated to this mobile station (physical access resources, or addresses in the case of shared resources). In the case of GSM, this corresponds to the connected mode for a connection with an MSC, and to the active mode of GPRS for a communication with an SGSN (“Serving GSN”).
The problem arises of the continuity of supply of the services normally provided to idle mobile stations when the latter are in active mode. A priori, provision may be made to allocate or to use dedicated channels or subchannels for exchanging the information regarding these services. This requires a certain coordination to manage the various items of information exchanged with the mobile station.
Some of the idle mode services are simply not supplied in active mode, such as for example the SMS-CB service in the known GSM networks.
In certain cases, the core network is responsible for the coordination. With a single switch, this implies that it must ensure the supply of the idle mode services to the active mobile stations. With several switches, this obliges them to cooperate for this purpose. An example of this is disclosed in WO97/26764, for the service of notification of incoming GSM calls to terminals in GPRS active mode. This type of coordination is very difficult to apply in a heterogeneous environment. In particular, it is problematic in the case of GSM since GSNs have been added to the MSCs, because the support of communication protocols between the MSCs and the GSNs is not mandatory. It is moreover a very complex process since it obliges the switches to know the configuration of the infrastructure and manage the consequences thereof.
Alternatively, the mobile stations may be responsible for the coordination. In the case of the GSM paging service, this is the solution mainly adopted hitherto so that the service can be supplied by an MSC for a mobile station communicating with an SGSN, or by an SGSN for a mobile station communicating with an MSC. The mobile station must then listen in to the idle mode resources, typically broadcasting channels, while it is otherwise in active mode. This type of solution leads to complex and expensive mobile stations and to non essential use of the precious access resources.
An object of the present invention is to provide a simple solution to the problem of the continuity of supply of services of idle mode type, and that this solution be readily compatible with various network organizations.